Silane coupling agents are compounds having in their molecule an organic functional group and a hydrolyzable group reactive with inorganic materials. Since the silane coupling agents are, due to their functional groups, capable of chemically bonding an organic polymer with an organic material, such as silica, thereby remarkably increasing the mechanical strength of the organic polymer, demand for them is increasing as an indispensable material in the development of ultrafashionable composite materials.
Gamma-aminopropyl alkoxy silanes are used in the art as the silane coupling agent, and it is known that they can be prepared by hydrosililation of an allylamine, which may be substituted on the nitrogen atom, with a hydro-alkoxy silane.
For example, Japanese Patent Laid-open Publication No. 60-81189 discloses a process for the preparation of aminopropyl alkoxy silanes, which comprises reacting an allylamine with a hydro-alkoxy silane using a platinum catalyst, such as chloroplatinic acid, in the presence of a promoter, such as anhydrous sodium carbonate. However, the reaction of an allylamine with a hydro-alkoxy silane in the presence of a platinum catalyst, such as chloroplatinic acid, inevitably produces the corresponding beta-aminopropyl alkoxy silane which may be referred to herein as the beta-isomer in addition to the desired gamma-aminopropyl alkoxy silane, which may be referred to herein as the gamma-isomer, normally with a ratio of the gamma-isomer to the beta-isomer of from 4 to 6, posing a problem in that the selectivity of the desired gamma-isomer is not satisfactorily high. An attempt to separate the gamma-isomer from the beta-isomer is not attractive, since it requires a distillation tower having a considerable number of distillation plates.
Japanese Patent Laid-open Publication No. 61-229885 discloses a process for the preparation of aminopropyl alkoxy silanes by reacting an allylamine with a hydro-alkoxy silane in the presence of a catalyst comprising rhodium-organic tertiary phosphine complex and optionally triphenylphosphine. By this process gamma-aminopropyl alkoxy silanes can be prepared in a high selectivity. The process is disadvantageous, however, in that a prolonged reaction time is required to achieve a high conversion. Further, an excessive amount of triphenylphosphine must be used to achieve a high selectivity of the gamma-isomer, leading to a possible contamination of the finally distilled product by the triphenylphosphine.